1. Field Of The Invention
The present invention relates to digital signal processing. More particularly the present invention relates to a method and apparatus for providing voice privacy in electronic communications systems.
2. Problems In The Art
In the field of two-way radio communications, it is often desired to have secure communications between the sender and receiver. The most common method of providing security in two-way radio communications is by scrambling the transmitted audio signals and descrambling the received audio signals. Prior art scrambling and descrambling methods have various disadvantages. Most prior art devices involve hardware with excessive complexity and result in poor audio quality after being descrambled. Most prior art scrambling and descrambling systems also are inefficient and require a significant amount of hardware to scramble and descramble the audio signals. Prior art systems typically require separate scrambling and descrambling circuits since the scrambling and descrambling processes are different.
Some prior art scrambling and descrambling methods use a "rolling code" to alter the scrambling method over time to reduce the chances of an unauthorized receiver descrambling the signals. Prior art systems using rolling code descramblers are limited in the frequency that the code changes without causing a distortion to the signal. Also, when prior art systems use a rolling code, spectral loss is observed.
Therefore there is room for improvement in the art. The present invention represents an improvement over the state of the art.
3. Features Of The Invention
A general feature of the present invention is the provision of a method and apparatus for providing voice privacy in electronic communications systems which overcomes problems found in the prior art.
A further feature of the present invention is the provision of a method and apparatus for providing voice privacy in electronic communications systems which uses a frequency translation to shift the spectrum of the signal, reduces the sampling rate, shifts the spectrum again, increases the sampling rate, shifts the spectrum again, and extracts the real part of the complex signal for transmission.
A further feature of the present invention is the provision of a method and apparatus for providing voice privacy in electronic communications systems which eliminates the need for tunable filters and the like by digitizing an audio signal and uses a digital signal processor (DSP) to process the signal.
A further feature of the present invention is the provision of a method and apparatus for providing voice privacy in electronic communications systems which creates a scrambled signal which can be efficiently and reliably sent through wireless communication systems or over telephone lines.
A further feature of the present invention is the provision of a method and apparatus for providing voice privacy in electronic communications systems which uses software to process the digitized audio signal rather than discrete analog components.
A further feature of the present invention is the provision of a method and apparatus for providing voice privacy in electronic communications systems which uses the identical process and hardware to scramble and descramble a signal.
A further feature of the present invention is the provision of a method and apparatus for providing voice privacy in electronic communications systems which preserves more of the original audio spectrum than previous methods.
A further feature of the present invention is the provision of a method and apparatus for providing voice privacy in electronic communications systems which improves the security of the transmission by allowing for more rapid changing of inversion frequencies than in previous methods.
These as well as other objects, features, and advantages of the present invention will become apparent from the following specification and claims.